The U. S. Navy uses Rolls-Royce gas turbines for ship service power on the DDG-51 class destroyer and the CG-47 class cruiser. Both engines have duplex thermocouples (T/Cs) and redundant T/C harnesses for turbine temperature monitoring and control. One harness provides an average of all the installed T/Cs, while the other provides the full authority digital control (FADC) with an individual signal from each. The legacy FADC algorithm allows up to four T/Cs to be out of average on the individual harness. Any additional T/C failures will cause the control to ignore the entire individual harness and rely on the averaging harness alone. This logic has inadvertently led to multiple over-temp conditions and subsequent engine removals. A change to control logic has been developed that aims to prevent these over-temp scenarios and is currently being introduced to the fleet. This paper will discuss in depth the cause of the over-temp, the examination of the control logic and the correction that is designed to prevent it from recurring.

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